Wrap the tofu block with a thick layer of paper towels, set it over a wire rack, and weigh down with a saucer or bowl for about 15 to 20 minutes to extract moisture.
Cut into cubes.
In a wide pan over medium heat about 2-inches deep of oil until hot but not smoking.
Add tofu in batches and cook, turning as needed, until golden and crisp. With a slotted spoon, remove from pan and drain on paper towels.
In a skillet over medium heat, heat about 1 tablespoon butter. Add onions and garlic and cook until slightly softened.
Add bell peppers and chili peppers and cook, stirring regularly, until tender-crisp.
Add calamansi juice and seasoning sauce. Simmer until slightly reduced.
Season with salt and pepper to taste.
Remove from heat. Add fried tofu cubes and mayonnaise. Toss just until evenly coated.
Transfer to a sizzling plate. Garnish with chopped chili peppers and serve immediately.
Notes
Remove from heat before adding the mayonnaise to prevent the dish from getting too greasy.